It may be stating the obvious to say it, but health systems are context-specific. Every country’s system is a hotch-potch of features. Some created by deliberate decisions; some stop gap-turned-permanent solutions; and many organic arrangements that have grown to fill gaps, with interesting arrays of unintended effects.

These systems usually have similar goals – to deliver effective, impactful health care equitably and accessibly – but the ways those goals are achieved are necessarily idiosyncratic. More often than not, it is the approach to implementation that determines eventual outcomes, rather than the intervention itself.

For these reasons, research that focuses on finding the “right” way to organise a health system by comparing settings is intellectually interesting but not necessarily directly useful for policy or programme design. There are many lessons that can be learnt by looking at the experiences of countries with common features, but aiming for generalizable conclusions often means finding the lowest common denominator – and losing much of the context-specific information that is crucial in determining results in the process.

The most policy-useful research is that which seeks to identify ideas and innovations with the potential to bring profound change if implemented on a large scale – and then delves deeper to understand why those ideas worked the way they did, in the place they did.

The science of systems, of real-world settings, is not so much about the what – the technical details of a policy change intervention – but about the how – what conditions led to success and how can they be replicated. Knowing which lessons and best practices can be effectively translated and scaled up – scalability – is the most valuable knowledge policymakers and programme designers can build on.